Adding songs through Droid File Transfer

So I got a new phone, and using Android File Transfer I tried moving my itunes library onto my phone. Well, of course, there was a hitch. On the Google Play Music app, they have the "Last Added" playlist serve as a general playlist with all your music. The only issue is it keeps saying that only 500 songs were added, despite my itunes library have roughly 650 songs on it. What's the deal? Do I need a new music app? Why can I not have all of my music?